We synthesized for the first time a series of emissive ring-shaped Re(I) complexes (Re-rings) with various numbers of Re(I) units and various lengths of bridge ligands. The photophysical properties of the Re-rings could be varied widely through changes in the size of the central cavity. A smaller central cavity of the Re-rings induced intramolecular π-π interactions between the ligands and consequently caused a stronger emission and a longer lifetime of the excited state. The Re-rings can function as efficient and durable photosensitizers. The combination of a trinuclear Re-ring photosensitizer with fac-[Re(bpy)(CO)3(MeCN)](+) (bpy = 2,2'-bipyridine) as a catalyst photocatalyzed CO2 reduction with the highest quantum yield of 82%.

No abstract

No abstract

Stepwise two-photon processes not only have great potential for efficient light harvesting but also can provide valuable insights into novel photochemical sciences. Here we have designed a [2.2]paracyclophane-bridged bis(imidazole dimer), a molecule that is composed of two photochromic units and absorbs two photons in a stepwise manner. The absorption of the first photon leads to the formation of a short-lived biradical species (half-life = 88 ms at 298 K), while the absorption of the additional photon by the biradical species triggers a subsequent photochromic reaction to afford a long-lived quinoid species. The short-lived biradical species and the long-lived quinoid species display significantly different absorption spectra and rates of the thermal back-reaction. The stepwise two-photon excitation process in this photochromic system can be initiated even by incoherent continuous-wave light irradiation, indicating that this two-photon reaction is highly efficient. Our molecule based on the bridged bis(imidazole dimer) unit should be a good candidate for multiphoton-gated optical materials.

Using a newly developed transmission-type photocathode, an electron beam of super-high brightness [ð1:3 AE 0:5Þ Â 10 7 AÁcm À2 Ásr À1 ] was achieved. Moreover, the spin-polarization was as high as 90%. We fabricated a transmission-type photocathode based on a GaAs-GaAsP strained superlattice on a GaP substrate in order to enhance the brightness and polarization greatly. In this system, a laser beam is introduced through the transparent GaP substrate. The beam is focused on the superlattice active layer with a short focal length lens. Excited electrons are generated in a small area and extracted from the surface. The shrinkage of the electron generation area improved the brightness. In addition, a GaAs layer was inserted between the GaP substrate and the GaAsP buffer layer to control the strain relaxation process in the GaAsP buffer layer. This design for strain control was key in achieving high polarization (90%) in the transmission-type photocathode. #

Articles you may be interested in30-kV spin-polarized transmission electron microscope with GaAs-GaAsP strained superlattice photocathode Development of spin polarized electron photocathodes: GaAs-GaAsP superlattice and GaAs-AlGaAs superlattice with DBR AIP Conf.In order to produce a high brightness and high spin polarization electron beam, a pointlike emission mechanism is required for the photocathode of a GaAs polarized electron source. For this purpose, the laser spot size on the photocathode must be minimized, which is realized by changing the direction of the injection laser light from the front side to the back side of the photocathode. Based on this concept, a 20 kV gun was constructed with a transmission photocathode including an active layer of a GaAs-GaAsP superlattice layer. This system produces a laser spot diameter as small as 1.3 m for 760-810 nm laser wavelength. The brightness of the polarized electron beam was ϳ2.0ϫ 10 7 A cm −2 sr −1 , which corresponds to a reduced brightness of ϳ1.0ϫ 10 7 A m −2 sr −1 V −1 . The peak polarization of 77% was achieved up to now. A charge density lifetime of 1.8 ϫ 10 8 C cm −2 was observed for an extracted current of 3 A.

No abstract

A new prototype of a zero voltage soft-switching (ZVS) utility frequency ac (UFAC) to high-frequency ac (HFAC) resonant power converter for induction heating (IH) applications is presented in this paper. The series resonant ac-ac converter proposed herein can process the frequency conversion without any diode bridge rectifier (DBR), thereby reducing the relevant conduction power losses. In addition, power factor correction (PFC) can be naturally achieved by the inductor-based boost halfbridge (BHB) circuit with the non-smoothed dc (NSDC)-link. The operation principle together with a IH load power regulation scheme is described, and the converter performances including ZVS operations and PFC are demonstrated in an experiment with a 3.0 kW-30 kHz prototype by comparing with the previouslydeveloped converter. Finally, the feasibility of the proposed ac-ac converter is evaluated from a practical point of view.Keywords-Utility-frequency (UF)-high frequency (HF) ac-ac power converter, diode full-bridge rectifier-less (bridgeless), boost half-bridge (BHB), non-smoothed dc (NSDC)-link, power factor correction (PFC), zero voltage soft-switching (ZVS), pulse-widthmodulation (PWM), induction heating (IH).